Sensitivity of Shiga Toxin–Producing Escherichia coli, Multidrug-Resistant Salmonella, and Antibiotic-Susceptible Salmonellato Lactic Acid on Inoculated Beef Trimmings

Studies were performed to determine whether lactic acid treatments used to reduce Escherichia coliO157:H7 on beef trimmings are also effective in controlling non-O157 Shiga toxin–producing E. coli(nSTEC), and multidrug-resistant and antibiotic-susceptible Salmonella. Beef trimming pieces (10 by 5 by 1 cm) were inoculated (3 log CFU/cm2) separately with four-strain mixtures of rifampin-resistant E. coliO157:H7, O26, O45, O103, O111, O121, and O145. Similarly, in a second study, trimmings were separately inoculated with rifampin-resistant E. coliO157:H7, and antibiotic-susceptible or multidrug-resistant (MDR and/or MDR-AmpC) SalmonellaNewport and SalmonellaTyphimurium. Inoculated trimmings were left untreated (control) or were immersed for 30 s in 5% lactic acid solutions (25 or 55°C). No differences (P≥ 0.05) were obtained among surviving counts of E. coliO157:H7 and those of the tested nSTEC serogroups on lactic acid–treated (25 or 55°C) samples. Counts (3.1 to 3.3 log CFU/cm2) of E. coliO157:H7 and nSTEC were reduced (P< 0.05) by 0.5 to 0.9 (25°C lactic acid) and 1.0 to 1.4 (55°C lactic acid) log CFU/cm2. Surviving counts of Salmonellaon treated trimmings were not influenced by serotype or antibiotic resistance phenotype and were similar (P≥ 0.05) or lower (P< 0.05) than surviving counts of E. coliO157:H7. Counts (3.0 to 3.3 log CFU/cm2) were reduced (P< 0.05) by 0.5 to 0.8 (E. coliO157:H7) and 1.3 to 1.5 (Salmonella) log CFU/cm2after treatment of samples with 25°C lactic acid. Corresponding reductions following treatment with lactic acid at 55°C were 1.2 to 1.5 (E. coliO157:H7) and 1.6 to 1.9 (Salmonella) log CFU/cm2. Overall, the results indicated that lactic acid treatments used against E. coliO157:H7 on beef trimmings should be similarly or more effective against the six nSTEC serogroups and against multidrug-resistant and antibiotic-susceptible SalmonellaNewport and SalmonellaTyphimurium.